The invention relates to a device for detecting impedance disturbance points in symmetrical data transmission lines.
DE-C2-42 05 241 has already disclosed a data transmission device by means of which a bidirectional, isolated data transmission can be carried out between a master stage and a slave stage. This takes place using a coupling loop and a Hall-voltage measuring device. The Hall-voltage measuring device is realized together with a signal processing circuit in the form of an integrated circuit. Data are sent back from the slave stage to the master stage using an interrupter stage which interrupts the current in the bus line in a defined way. An evaluation of the pulse duty ratio in a comparison circuit of the master stage makes it possible to detect a reported-back logical status.
The applicant""s EP-A1-0 875 995 likewise discloses an integrated data transmission circuit with potential separation between the input circuit and output circuit. The input circuit has an input for binary input signals. The output circuit contains an integrated, magnetosensitive coupling element and at least one output which is driven by the coupling element and via which binary output signals can be emitted. To permit the data transmission mentioned, line means are provided in order to conduct input signals into the proximity of the coupling element in a way separating the voltage potentials in the input circuit and output circuit. An integrated Hall generator may be used as the coupling element.
In the case of symmetrical, shielded and unshielded data transmission lines, disturbances may occur during operation, attributable to short circuits or line interruptions. Disturbances of this type have until now been detected and localized by using service personnel in offline operation. This involves using complicated measuring instruments and making use of the personnel""s expertise.
Setting out from this prior art, the invention is based on the object of showing a new way in which the detection of impedance disturbance points in symmetrical data transmission lines can be improved.
This object is achieved by a device with the features specified in claim 1. Advantageous refinements and developments of the invention emerge from the dependent claims.
The advantages of the invention are, in particular, that the claimed detection of impedance disturbance points takes place in an isolated manner. The modules necessary for realizing the evaluation unit can be made in the form of an integrated circuit. This makes it possible in a simple way for the lines to be permanently monitored during operation without any reactions, so that disturbances occurring are automatically signaled by the output of an associated fault signal. The invention can be used for example in all bus systems with differential signal transmission, for example what is known as the Profibus.